1. Field
This disclosure relates generally to circuits, and more specifically, to charge pumps.
2. Related Art
Charge pumps play an important role in a variety of integrated circuits. There are a number of situations where a higher voltage is needed than the power supply voltage. This has become even more significant as power supplies are reducing in magnitude. One example is integrated circuits that include non-volatile memories (NVMs) that are programmed and/or erased. Integrated circuits that are mostly digital but include some analog circuits will sometimes operate the analog circuits at a voltage higher than is needed for the digital circuits. The particular elevated voltage may differ based on the particular application as defined by the user. Thus, it may be useful to be able to vary the magnitude of the elevated voltage. Also the power supply voltage can vary. The power supply can in some cases vary quite significantly, such as from 0.9 volt to 5.0 volts. One of the difficulties with charge pumps is that for a given circuit, the output voltage provided is not linear with respect to time and the voltage provided is provided in increments based on the capacitances being utilized. The increments can be smoothed by reducing the capacitance and increasing the clock frequency but this is limited due to inefficiency becoming a bigger problem at higher frequencies because second and third order effects become more significant at higher frequencies and can even dominate.
Thus there is a need for a charge pump that improves upon one or more of the issues raised above.